WINGS OF INSECTS. 305 



winged genera. The Flea, however, cannot on this account be looked 

 upon as any other than the imago or complete insect, for it will be 

 found to have undergone all the preparatory changes. The Flea, when 

 it issues from the egg, is in fact a worm-like and footless larva, in which 

 condition it lives about twelve days. When about to become a pupa, it 

 spins for itself a little silky cocoon, wherein it conceals itself until, 



Fig. 153. 



Pulex irritans. 



Caving thrown off its last skin, it appears in its mature form, deprived 

 indeed of wings, that, under the circumstances in which it lives, would 

 be useless appendages, but still, with this exception, corresponding in 

 every particular with other insects in their imago state. 



(797.) The wings of insects differ much in texture. In the Neuro- 

 ptera, by far the most powerful fliers met with in the insect world, all 

 four wings are of equal size, and consist of a thin membranous expansion 

 of great delicacy and of a glassy appearance, supported at all points by 

 a horny network (fig. 146). Few things are met with in nature more 

 admirable than these structures ; they present,, indeed, a combination of 

 strength and lightness absolutely unequalled by anything of human in- 

 vention ; and as instruments of flight they far surpass the wings of birds, 

 both in the power and precision of their movements, inasmuch as these 

 insects can fly in all directions backwards, or to the right or left, as 

 well as forwards. Leeuwenhoek* narrates a remarkable instance in 

 which he was an eye-witness of the comparative capabilities of the 

 Dragon-fly and the Swallow, as relates to the perfection of their flight. 

 The bird and the insect were both confined in a menagerie about a 

 hundred feet long, and apparently their powers were fairly tested. The 

 swallow was in full pursuit ; but the little creature flew with such asto- 

 nishing velocity, that this bird of rapid flight and ready evolution was 

 unable to overtake and entrap it, the insect eluding every attempt, 

 and being generally six feet before it. " Indeed," say the authors 

 from whom we quote the above anecdote f, " such is the power of the 

 long wings by which the Dragon-flies are distinguished, and such the 



* Epist, 6, Mart. 1717. t Kirby and Spence, op. cit. vol. ii. p. 351. 



x 



